### How much gold is there in our sun?

• XKCD 1944 claims that there is "more gold in the sun than water in the oceans". Is this really true?

Who here would dare contradict xkcd.com ? :-)

Alt text for people that don't want to click through to XKCD: _"The retina is the exposed surface of the brain, so if you think about a pot of gold while looking at a rainbow, then there's one at BOTH ends."_

@StephenG Much as I hate to contradict XKCD, that's not how rainbows work. You don't get a partial rainbow if there's simply a cloud in the right position. It has to be raindrops.

Also discussed in the xkcd forum.

4 years ago

The mass of the sun is 1.989 × 1030 kg.

Abundance in the Sun of the elements gives a percentage 1 × 10-7 % for gold *, so that leaves you with a mass of 1.989 × 1021 kg of gold.

HowStuffWorks states that there is 1.26 × 1021 kg water on Earth, of which 98% is in the oceans, i.e. 1.235 × 1021 kg.

This would mean the XKCD statement is true: there is 1.6 times as much gold in the sun as there is water in the oceans.

* They cite WolframAlpha as their source. Executing SolarAbundance "Gold" there confirms this (mass) percentage.

There are at least two problems with that calculation: (1) The source for abundance doesn't say whether the percentage is of mass or of number of atoms; (2) if is it percentage of mass, 1 × 10-7 % means somewhere between 0.5 × 10-7 % and 1.5 × 10-7 %, so the proportion could be as low as 0.8, which is less than 1.

How did that gold get there? I am under the impression that, as a main sequence star, the sun cannot create its own gold through element synthesis. So I am guessing that the gold in the sun was present when the sun first started burning, and I guess it must come from older generation supernovae?

@ChocolateAndCheese Correct, virtually all of the elements heavier than Helium in the Sun (and the rest of the solar system) are the remains of older stars.

@ Peter Taylor, similarly, the XKCD cartoon doesn't state whether it is more by mass or more by number of atoms/molecules.

@Octopus or by volume. 2 lbs of gold is quite a bit smaller than 1 lb of sea-water.

@ChocolateAndCheese yes -- the same way it got in the earth :)

What is the uncertainty of this abundance-of-gold-in-the-Sun estimate? Without uncertainty estimates, the question which one is more cannot be answered.

"1 × 10-7 %" sound really weird. Would 1 part per billion be better, or do we run into American versus British English problems?

@gerrit That is always the case. Mathematically speaking, since the abundance is given with only one significant digit, the answer should be too. But we are talking about a comic here, not a scientific publication.